1. Technical Field
Embodiments relates to a semiconductor memory device, a memory system including the same, and an operating method thereof.
2. Related Art
A semiconductor memory device is a memory device typically implemented by using a semiconductor material, such as for example, silicon (Si), germanium (Ge), gallium arsenide (GaAs), and indium phosphide (InP). The semiconductor memory device is generally classified as a volatile memory device or a nonvolatile memory device.
A volatile memory device is a memory device where the stored data dissipates when a power supply to the volatile memory device is discontinued. Examples of volatile memory devices include, but are not limited to, a Static RAM (SRAM), a Dynamic RAM (DRAM), and a Synchronous DRAM (SDRAM). A nonvolatile memory device is a memory device where the stored data is maintained when a power supply to the nonvolatile memory device is discontinued. Examples of nonvolatile memory devices include, but are not limited to, a Read Only Memory (ROM), a Programmable ROM (PROM), an Electrically Programmable ROM (EPROM), an Electrically Erasable and Programmable ROM (EEPROM), a flash memory, a Phase-change RAM (PRAM), a Magnetic RAM (MRAM), a Resistive RAM (RRAM), and a Ferroelectric RAM (FRAM). Flash memories are generally classified as a NOR type flash memory device or a NAND type flash memory device.
The flash memory device may be a 2-dimensional semiconductor device where strings are formed in parallel on a semiconductor substrate or a 3-dimensional semiconductor device where strings are vertically formed on a semiconductor substrate.
The strings in a 3-dimensional semiconductor memory device include a drain select transistor, memory cells, and a source select transistor electrically coupled between a bit line and a source line.
The 3-dimensional semiconductor device may include charge trap memory cells. In such a 3-dimensional semiconductor device, a Contents Addressable Memory (CAM) cell for storing CAM data is a charge trap memory cell. In some cases, when a charge trap memory cell is utilized as a CAM cell, the CAM data is programmed in the CAM cell when the CAM cell is in an erase state prior to packaging a memory chip. Electrons may be trapped within the charge trap memory cell being used as a CAM cell. When a CAM cell programmed with CAM data is subjected to relatively high temperatures associated with the packaging process, the electrons may move within a charge storage layer of the CAM cell or may recombine with holes in the charge storage layer. A threshold voltage within the charge trap memory cell may be changed.